Fluorescent technique is widely used among others in chemical, biochemical, medical, chemical research fields for analyzing organic compounds, detection of particular compounds in a complex, differentiating malignant cell from benign, with exquisite sensitivity and selectivity.
Fluorescent technique is now extended to develop photo luminescent devices for detecting explosives, in heavy chemical industry, mines, etc. such as sensing gas leakages and as chemo sensors and the like.
Article titled, “Fluorescent probe for Fe(III) based on pyrene grafted multiwalled carbon nanotubes by click reaction” by Li Jing, Cong Liang, Xinhao Shi, Siqiu Ye and Yuezhong Xian in Analyst, 2012,137, 1718-1722 reports the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with pyrene via Cu(I)-catalysed azide/alkyne click (CuAAC) reactions under mild conditions to afford the nano composites of pyrene-MWCNTs. Fourier transform infrared spectroscopy (FT-IR), ultraviolet and visible spectroscopy (UV-Vis), and fluorescence spectroscopy were used to characterize the nano composites of pyrene clicked MWCNTs. The nano composites of pyrene clicked MWCNTs are used in photo luminescent devices as a highly sensitive and selective fluorescence “turn-off” sensor for Fe3+. Article titled “Pyrene-Containing Conjugated Polymer-Based Fluorescent Films for Highly Sensitive and Selective Sensing of TNT in Aqueous Medium” by Gang He, Ni Yan, Jiayu Yang, Hongyue Wang, Liping Ding, Shiwei Yin, and Yu Fang in Macromolecules, 2011, 44 (12), pp 4759-4766 reports the synthesis and characterization of two poly(pyrene-co-phenylene ethynylene)s of different compositions (PyPE-1 and PyPE-2). The two polymers were casted, separately, onto glass plate surfaces to fabricate films (film 1, film 2) for sensing performance studies. The fluorescence emissions of the two films were observed to be sensitive to the presence of 2,4,6-trinitrotoluene (TNT) in aqueous phase, however, TNT showed little effect upon the emission of the parent polymer, poly(phenyleneethynylene) (PPE). The difference was accounted for (1) the π-π interaction between pyrene moieties contained in the copolymers and the analyte, TNT, molecules, and (2) more suitable matching of the LUMOs (lowest unoccupied molecular orbital) of the pyrene-containing conjugated polymers with that of TNT molecules. Further experiments demonstrated that the sensing is reversible and rarely encounters interference from commonly found compounds, including other nitroaromatics (NACs). Fluorescence lifetime measurements revealed that the quenching is static in nature.
Article titled ‘Pyrenyl Excimers Induced by the Crystallization of POSS Moieties: Spectroscopic Studies and Sensing Applications’ by Hua Bai, Chun Li et. al in ChemPhysChem 2008, 9, 1908-1913; DOI: 10.1002/cphc.200800149 reports fluorescent sensors based on thin PBPOSS films for the rapid detection of TNT. The spin-coated thin films of PBPOSS emit strong blue light at 475 nm when excited at 350 nm because of the formation of a high content pyrenyl excimers induced by the crystallization of POSS moieties. As PBPOSS being small molecule, it cannot however form self -standing film.
Article titled ‘Optical properties of pyrene and anthracene containing imidazoles:Experimental and theoretical investigations’ by Dhirendra Kumar, K. R. Justin Thomas published in Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 162-173 reports a series of imidazole derivatives containing anthracene and pyrene segments useful to design imidazole dyes with higher wavelength absorptions for photovoltaic applications. The imidazole derivatives containing anthracene and pyrene segments show red-shifted absorption and emission profiles due to extended conjugation. The article does not disclose the use of polymer film possessing pyrene and anthracene fluorophores for the detection of nitroaromatics (NACs).
Article titled ‘Pyrene-Containing Conjugated Polymer-Based Fluorescent Films for Highly Sensitive and Selective Sensing of TNT in Aqueous Medium’ by Gang He, Ni Yan et al published in Macromolecules, 2011, 44 (12), pp 4759-4766 relates to two poly(pyrene-co-phenyleneethynylene)s of different compositions (PyPE-1 and PyPE-2) for sensing performance studies. The fluorescence emissions of the two films were sensitive to the presence of 2,4,6-trinitrotoluene (TNT). The thin films of polymer were fabricated by spin-coating technique which may not be self-standing; further the sensing was demonstrated in solution (aqueous phase).
In light of the potential applicability of fluorophores in photoluminescent devices as a highly sensitive and selective fluorescence, there remains a need in the art to provide composition with enhanced photoluminescence by coupling them with highly-conjugated polymer having bright luminescence and bipolar transport characteristics. Thin-film sensors are widely acceptable due to reusability and ease in device making. Therefore, thin films possessing excimer emission are very promising materials as fluorescence sensors.
However, preparation of self-standing polymeric ionic liquid (PIL) thin films with strong excimer emission is challenging as many factors exert influences on fluorescence properties of the fluorophores such as biomolecular structures, proximity and concentrations of quenching species, pH of the solvent, stability etc. Further, physical entrapment of the fluorescent probe in a polymer matrix produces inhomogeneity in the material and leads to stability issues due to the leaching of the fluorescent probe, reducing the lifetime and reproducibility of the sensor. The most preferred method to prevent decay of excimer emission is the covalent attachment of fluorophore in the polymer matrix.
Polymers such as Polybenzimidazole (PBI) or ABPBI are known for their rigidity, thermo-chemical and mechanical stability. The promising properties of these polymers render them suitable for incorporating fluorophores which can prevent decay of excimer emission during covalent attachment to flurophore in polymer matrix due to rigid backbone and bipolar transport characteristics.
Furthermore, polymeric materials exhibiting high CO2 sorption are known in the art as sorbent and gas separation membrane material.
There is a publication, WO2012035556, of the present applicant which discloses Polybenzimidazole (PBI) based polymeric forms of ionic liquids as CO2 sorbent and gas separation membrane materials, however does not disclose the fluorescent property and applicability for detecting explosives.
In light of the above, the present inventors felt a need to provide stable polymeric form of ionic liquid composition that possesses both enhanced fluorescence useful in detection of explosives and high degree of gas permeation capacity.